1. Field of Invention
The present invention relates to a driving method and a driving circuit of an electro-optical device that performs a tone display control by modulation on the time axis and an electro-optical device and electronic equipment.
2. Description of Related Art
Electro-optical devices, such as liquid crystal display devices using liquid crystal as an electro-optical material, are widely used in display units of various information processors, liquid crystal television sets and the like as display devices. Such devices are taking the place of cathode-ray tubes (CRTs).
For example, a conventional electro-optical device includes pixel electrodes which are arranged into a matrix, an element substrate having switching elements such as TFTs (thin film transistors) coupled to the pixel electrodes, an opposing substrate on which counter electrodes which oppose the pixel electrodes are formed, and a liquid crystal serving as an electro-optical material which is filled between both substrates. In such a structure, when scanning signals are applied to the switching elements through scanning lines, the switching elements conduct. While the switching elements are conducting, when image signals of voltages according to the desired tone are applied to the pixel electrodes through data lines, electrical charge according to the voltages of the image signals accumulates in the liquid crystal layer formed between the pixel electrodes and the counter electrodes. Once the electrical charge has accumulated, the accumulation of electrical charge in the liquid crystal layer is maintained due to the liquid crystal layer's own capacitance or the accumulated capacitance even if the switching elements are turned off. When the switching elements are driven to control the amount of accumulated charge according to the desired tone in this way, the orientation of the liquid crystal varies from pixel to pixel, and the density varies from pixel to pixel. A tone display is therefore possible.
The electrical charge may accumulate in the liquid crystal layer of the pixels for only a portion of a period. Hence, the process to, first, use a scanning line driving circuit to sequentially select the scanning lines, second, use a data line driving circuit to sequentially select the data lines for a period during which the scanning lines are selected, and, third, sample the image signals of voltages according to the desired tone for the selected data lines enables time-divisional multiplex driving in which the scanning lines and the data lines are commonly used by a plurality of pixels.
However, the image signals applied to the data lines refer to voltages according to the desired tone, namely, analog signals. This requires a D/A converting circuit, an operational amplifier, etc. as peripheral circuits of the electro-optical device, leading to increased cost of the overall device. Furthermore, since a nonuniform display can be caused by nonuniformity in characteristics of the D/A converting circuit, the operational amplifier, etc., various wiring resistances, etc., there is a problem in that it is extremely difficult to achieve a high-quality display. This problem is noticeable in particular when a high-definition display is desired.